Electrical apparatus having fuse and insulated and sealed electrical connections



Oct. 28, 1969 D. J. RISTUCCIA 3,475,693 ELECTRICAL APPARATUS HAVING FUSE AND INSULATED AND SEALED ELECTRICAL CONNECTIONS Filed July 18, 19s? INVENTOR Donald J. Ristuccio ATTORNEY 3,475,693 ELECTRICAL APPARATUS HAVING FUSE AND INSULATED AND SEALED ELEC- TRICAL CONNECTIONS Donald J. Ristuccia, Sharpsville, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 18, 1967, SerrNo. 654,220

I Int. Cl. Htlih 85/02 US. Cl. 337207 15 Claims ABSTRACT OF THE DISCLOSURE Electrical inductive apparatus, such as a transformer, including a casing filled to a predetermined level with liquid dielectric, a magnetic core-winding assembly disposed within said casing, protective fuse apparatus disposed through the cover or wall of said casing, and at least one high voltage bushing assembly disposed through the side wall or cover of the casing. The high voltage bushing is electrically connected to the protective fuse apparatus, with an electrically insulated and sealed electrical conductor, and the conductors connections to the high voltage bushing and to the protective fuse apparatus are also electrically insulated and sealed. The protective fuse apparatus includes a tubular receptacle having a continuous opening extending between its ends, with one end being accessible outside the casing, and the other end extending into the casing and the liquid dielectric. The protective fuse apparatus also includes a removable fused portion accessible from outside the casing. The removable fused portion seals the upper end of the receptacle when it is in assembled relation with the receptacle, and it is sized to :allow the liquid dielectric to enter the receptacle.

CROSS-REFERENCE TO RELATED APPLICATION This application is related to application Ser. No. 580,- 285, filed Sept. 19, 1966 by M. G. Leonard, which application is assigned to the same assignee as the present ap] lication.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to electrical inductive apparatus,

such as transformers, and more particularly to electrical inductive apparatus of the type having a fusible link connected between the high voltage bushing, or bushings, and the high voltage winding.

Description of the prior art SUMMARY OF THE INVENTION Briefly, the present invention is a new and improved electrical inductive apparatus of the type having a casing filled to a predetermined level with liquid dielectric means, a magnetic core-winding assembly disposed Within the casing, protective fuse apparatus having a tubular receptacte and removable fusible link, and at least one high United States Patent ice voltage bushing. The high voltage bushing is sealingly disposed through an opening in the casing. The tubular receptacle of the protective fuse apparatus is also sealingly disposed through an opening in the casing, with its fusible link insertable and removable from outside the casing. The lower end of the receptacle extends into the liquid dielectric, passing through at least a portion of the air space disposed above the liquid dielectric. The operating handle of the fusible link seals the upper end of the receptacle when it is in assembled relation therewith, and the fusible link is sized to allow the liquid dielectric to enter the submerged end of the receptacle. The fusible link has electrodes which make contact with first and second electrical contacts sealingly disposed through the side wall of the receptacle. A first electrically insulated and sealed conductor connects the high voltage bushing with the first electrical contact of the receptacle, and a second electrical conductor connects the second electrical contact of the receptacle with the winding assembly of the inductive apparatus. In addition to the first electrical conductor being electrically insulated and sealed, its connections to the high voltage bushing and to the first electrical contact of the protective fuse apparatus are also electrically insulated and sealed. Thus, when the fusible element of the protective fusible apparatus melts, all live parts within the casing are electrically insulated and sealed, preventing an are from developing from the live parts to ground, through the ionized gas bubble formed by the interruption arc. Further, the construction of the protective fuse, wherein the axial or inner opening in the receptacle is sealed at its upper end and open at its lower submerged end, creates a diving bell effect, which prevents the ionized gas bubble produced during are interruption from entering the receptacle as it rises in the liquid dielectric. When the circuit is interrupted, the ionized gas bubble produced is ejected from the fusible link and from the receptacle, due to the construction of the fusible link wherein it is sealed at its upper end and open at its lower end, and when the ionized bubble starts to rise, it will not enter the receptacle due to its construction wherein its upper end is sealed.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description and drawing, in which the single figure illustrates electrical inductive apparatus constructed according to the teachings of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hereinbefore referred to co-pending application discloses a new and improved protective fuse apparatus suitable for use with electrical inductive apparatus, such as transformers. This protective fuse apparatus, however, is rated 1000 amperes symmetrical at 7600 volts, and is not used to interrupt currents higher than 1000 amperes. Thus, in most applications, this protective fuse apparatus is used with additional protective apparatus, in order to assure arc interruption, as most applications have a capability of more than 1000 amperes during short circuit conditions.

The present invention discloses new and improved transformer and protective fuse apparatus which makes it possible to rate the fusible link at 3500 amperes symmetrical at 7600 volts, thus making it entirely suitable as the sole protective device for the transformer against short circuits. In applications which have higher than 3500 amperes short circuit capability, the disclosed construction makes it practical to easily add a current limiting fuse, to provide the additional protection.

Referring now to the drawing, the single figure illustrates electrical inductive apparatus 10, such as a transformer. Electrical inductive apparatus includes a casing, only a portion of which is shown for purposes of illustration, which portion may be the cover of the casing, or any other suitable portion. Transformer 10 includes a liquid dielectric 14, disposed within casing 12 to a predetermined level 16, leaving an air space 18 over the liquid dielectric. A magnetic core-winding assembly 20, which may include high and low voltage windings 22 and 24, respectively, disposed in inductive relation with a magnetic core 26, is disposed within casing 12 and immersed in the liquid dielectric 14. Low voltage winding 24 is connected to a plurality of low voltage terminals or bushing assemblies, such as bushings 28, 30 and 32, with the magnetic core-winding assembly 20 and low voltage bushings 28, 30 and 32 being shown schematically, since they may be of any conventional form.

The high voltage winding 22, which in this instance is shown with one end grounded at ground 34, has its other end connected through protective fuse apparatus 40 to a high voltage bushing assembly 50. Also shown is a current limiting fuse 60, connected between winding 22 and fusible link 40, which may be used in certain applications, as will be hereinafter explained. The high voltage winding 22, while illustrated as having one end grounded, may also be of the type wherein each end is connected to the line through high voltage bushings. Since, in this instance, each protective link and high voltage bushing, will be constructed and connected in a similar manner, only one protective link and high voltage bushing assembly is shown in the drawing for purposes of simplicity.

The protective fuse apparatus 40 has two major parts, a receptacle or holder 42, and a removable fusible portion 44. The receptacle 42 includes an elongated tubular body member 46 having first and second ends 52 and 54, respectively, with a central or axial opening 56 which extends between its ends. Body member 46 is formed of an electrical insulating material, such as glass polyester, or a filament wound glass fiber impregnated with an epoxy resin system. Integrally secured to insulating member 46 is a sleeve member 58, formed of brass or other suitable metal, which extends for a predetermined distance into opening 56 from the first end 52 of member 46. Metallic sleeve member 58 contains threads on its inner diameter for receiving and securing the removable fusible portion 44.

Body member 46 starts at end 52 with a predetermined outside diameter 64, which is threaded as shown at 62, and then its outer diameter increases sharply to a larger outside diameter 66, forming a flange 68. An opening 70 is provided in casing 12, which is sized to receive the threaded diameter 64. A gasket member 72 may then be placed on flange 68, end 52 may be inserted through opening 70 from the inside of the casing 12, and a metallic nut member 74 having a threaded inside diameter, cooperates with threads 62 to snugly and sealingly secure receptacle 42 to the casing 12.

In addition to the axial opening 56, insulating body member 46 includes first and second transverse openings 76 and 78 through its side wall portion, spaced a predetermined axial distance apart near its end 54. Openings 76 and 78 provide access openings for first and second electrical contact assemblies 80 and 82, respectively. First and second electrical contact assemblies 80 and 82 have spring loaded contact members 84 and 86, respectively, connected to first and second electrical conductors 88 and 90, respectively. Since electrical contact assemblies 80 and 82 are similar in construction, only contact assembly 80 will be described in detail.

1 Electrical contact assembly 80 includes an insulating body portion or housing 92, which may be formed in two half sections of a glass polyester, or like insulating material, and when the two half sections are assembled they form a central bore or opening formed by three connecting chambers 94, 96 and 98. Chamber 94 includes the ,4 first electrical contact member 84, formed of copper or other good electrically conductive'material, which has a main contact portion 85 connected to a shaft portion87, shaft portion 87 extends into the second chamber 96. A spring 100, which may be formed of stainless steel, is disposed about shaft portion 87 in chamber 94, which urges electrical contact member 84 into" the opening 76 in the side wall portion of 'member'46. A flange 89 which extends radially outward from shaft 87 is disposed in chamber 96, which prevents the contact member 84 from traveling too far into opening 56, when the fusibleportion 44 is not in its assembled position. The electrical conductor 88 includes an electrically conductive wire 163 which enters housing 92 through chamber 98, and it continues into chamber 96 where it is brazed, or otherwise suitably secured to the shaft end of the electrical contact member 84.

Housing 92, at the startof its chamber 94, has a diameter which snugly fits into opening 76 of receptacle 42, and then it flares outwardly to form a flange 102. 'A gasket member 104 is disposed between the flange 102 and body member 46,.and suitable fastening means, such ashosetype clamps 106 and 108, may encircle the flange 102 and body member 46 to sealingly secure the electrical contact assembly 80 to receptacle 42.

The removable portion 44 of the protective fuse apparatus 40 includes a fusible link 110 having a tubular insulating body portion 112, formed of fiber, or other suitable insulating and are quenching material. Portion44 also includes first and second spaced electrodes or contacts 114 and 116, respectively, a fuse element or Wire 118 which is connected from the first electrode 114 through the inner diameter of body portion 112, to where the wire 118 leaves the inner diameter of body portion 112, and is connected to the second electrode 116. When the removable portion 44 is in assembled relation with receptacle 42, the first and second electrodes 114 and 116 make electrical contact with the first and second electrical contacts 84 and 86, respectively. The tubular body portion 112 has its central opening sealed at its upper end, and it is open at its lower end, in order to expel the ionized gas bubble formed during circuit interruption in a downward direction. 7

The first electrode 114 may include an outwardly extending tang 120 having an opening therein, for fastening the fusible link 110 to rod member 122 with a bolt, or other suitable fastening means. Rod member 122 is formed of an electrical insulating material, such as fiber. Insulating rod member 122 is secured to a metallic handle portion 126, formed of a suitable material such as brass,

which includes an opening 128 at its. outer end for receiving a'hook-stick, a flange 130 which compresses a gasket member 132 against end 52 of receptacle 42, a groove 134 for containing a shaft seal in the form of an O-ring 136, and threaded areas 138 and 140 for mating with the threads on the sleeve member 58of receptacle 42.

The protective fuse apparatus 40 may be mounted on the cover of casing 12, or a suitably formed side wall portion, wherein receptacle 42 may enter the liquid dielectric 14 for a predetermined distance, and also traverse at least a portion of the air space 18 above the liquid dielectric. Further, the rod member 122 and fusible link 110 should be radially sized to allow the liquid dielectric 14 to enter the submergerd end 54 of member 46 providing an air space 144 within the recepta-- Z 'as shown, of a cast solid resinous insulating system, such as an epoxy resin, having an axially extending stud or conductor portion 148. The weather end of the bushing assembly 50 may be of the type which has means 150 for cooperating with a plug-in type high voltage connector (not shown), or any other type of connecting means, depending upon the particular application transformer, and means on the encased end for connection to conductor 88, such as a nut 152 which is threaded on stud member 148. High voltage bushing assembly 50 has a flanged portion 154 intermediate its ends, and also may have threads 156 molded into its body portion 146 adjacent the flange 154 on the encased side of the bushing. Bushing 50 may be inserted into a suitable opening 158 in casing 12, in the cover or side wall portion, sealed with gasket member 160 disposed between the flange 154 and the casing 12, and secured in assembled relation with the casing 12 by a spring-grip nut member 162 which is threaded onto threads 156.

In addition to providing a seal at the upper end of receptacle 42, it is critical that all parts within the casing 12 which will still be at line potential after the wire of the fusible link has ruptured, be not only electrically insulated, but sealed with oil tight seals.

For example, conductor 88 which connects high voltage bushing 50 with the protective fuse apparatus 40 should be an insulated wire 163 having a tight fitting insulation 164 disposed thereon. Further, the electrical connection of the wire 163 to stud 148 of high voltage bushing 50, and the electrical connection of wire 163 to electrical contact 84, should be electrically insulated and sealed.

As shown in the figure, the connection of wire 163 to contact member 84 may be electrically insulated and sealed with a heat shrinkable tubing 170, which is either mastic lined, or which has an adhesive, such as an epoxy, applied to the parts to be covered prior to heat shrinking the tubing 170. The heat shrinkable tubing 170 should extend over the contact housing 92, and over the insulation 164 on the wire 163, to insure oil tight seals.

Heat shrinkable tubing may be used in a like manner to electrically insulate and seal the electrical connection between wire 163 and the stud 148 of high voltage bushing assembly 50. However, as shown in the figure, an inexpensive but effective seal may be formed by placing an insulating tube 172 over the encased end of the body portion 146 of high voltage bushing member 50, and then connecting the wire 163 to the stud 148 with the nut 152. The tubular member 172 should fit snugly against body portion 146, and extend outwardly from the end of the bushing to adequately encompass the electrical connection, and at least a portion of the wire 163 which has insulation 164 thereon. Then, electrical insulating means 176, such as an epoxy resin, may be poured into the chamber formed by the outwardly extending tube 172, which when cured forms a solid electrical insulating system which both insulates and seals the electrical connection between the conductor 88 and the high voltage bushing 50. An alternative to insulating and sealing the connection of conductor 88 to bushing assembly 50 would be to provide a hollow extension to the lower end of the bushing 50, such as would be provided by tube 172 without solid insulating means 176. If tube 172 were to be sealed and secured to the lower end of bushing assembly 50, the chamber produced about the enclosed electrical connection would provide a diving bell etfect, preventing the ionized gas bubble from the protective fuse apparatus from rising into the tubular enclosure.

If the inductive apparatus is a transformer, and a through current is required for a loop feed, a bushing similar to bushing assembly 50 may be provided, with a conductor being connected between the stud 148 of bushing assembly 50, to the similar stud of the additional bushing. The additional conductor should also be electrically insulated and sealed throughout its length, and at its connection oints with the bushing studs. In this instance, the

solid insulation 176 will electrically insulate and seal both the electrical connections to stud 148, and the connection of the additional conductor to the stud of the additional bushing may be electrically insulated and sealed in a like manner. Or, both bushings could be provided with tubular extensions in order to prevent ionized gas from rising into the enclosed volume and prevent it from coming into contact with the electrical potential.

Thus, by sealing and electrically insulating all parts which will have an electrical potential thereon after the fusible link performs its protective function, by making the receptacle 42 for the fusible link continuous from its lower opening 56 to the casing 12, and by extending the receptacle 42 into the dielectric fluid 14, the interrupting rating of the fusible link may be increased from 1000 amperes to 3500 amperes symmetrical at 7600 volts. This upgrading of the fusible link makes it practical to use the fusible link, as constructed by the teachings disclosed herein, as the sole protective device for protecting inductive apparatus in most applications against short circuit or fault currents.

In those-applications where the short circuit current may exceed 3500 amperes, current limiting fuse 60 may be added, between the protective fuse apparatus 40 and the high voltage winding 22. By connecting current limiting fuse 60 in this location, the electrical connections thereto need not be specially insulated and sealed. The current limiting fuse 60 may be used to extend the interrupting rating of the inductive apparatus to 20,000 amperes symmetrical at 7600 volts. Since most faults will be of a magnitude within 3000 amperes, the fusible link 110 will clear the fault, only requiring that the fusible link wire 118 be replaced, which is easily and inexpensively accomplished without removing the cover from the casing 12, by merely unscrewing the removable fusible portion 44 and removing it from its receptacle 42. A new fusible link 110 may then be installed and the removable portion 44 may be reinserted and turned down, to complete the primary circuit and seal the casing.

In summary, the invention substantially upgrades the rating of prior art photective fusible apparatus by first utilizing the diving bell effect, to insure that the ionized bubble, produced when the fusible link interrupts the circuit, will not enter the lower end of the receptacle as it rises in the liquid dielectric. Then, this ionized bubble is prevented from causing an arc from live parts within the casing of the apparatus to grounded parts, by not only electrically insulating all live parts, but by sealing the live parts to make them oil tight.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. Electrical inductive apparatus comprising a casing filled to a predetermined level with a liquid dielectric,

a magnetic core-winding assembly positioned within said casing and surrounded with said liquid dielectric,

protective fuse apparatus including a tubular receptacle and a removable fused portion, said receptacle being fixed to said casing and extending through an opening therein into said liquid dielectric, said receptacle having first and second electrical contacts immersed in the liquid dielectric, said removable fused portion sealing the upper end of said tubular receptacle and having first and second electrodes in removable contact with said first and second electrical contacts, respectively, said removable fused portion being sized to allow said liquid dielectric to enter said receptacle,

at least one electrical bushing assembly fixed to said casing and extending through an opening therein into said liquid dielectric, said bushing assembly having an axially extending conductor, one end of which is immersed in the liquid dielectric,

a first conductor electrically connecting the encased end of the conductor of said electrical bushing assembly to the first electrical contact of said receptacle,

a second conductor electrically connecting the second electrical contact of said receptacle to said winding assembly,

first insulating means electrically insulating and seal ing said first electrical conductor, including its electrical connection to the first electrical contact of said receptacle,

and second insulating means electrically insulating and sealing the electrical connection between said first conductor and the encased end of the conductor of said at least one electrical bushing assembly.

2. The electrical inductive apparatus of claim 1 wherein at least the electrical connection between the first electrical conductor and the first electrical contact of the receptacle is electrically insulated and sealed with a heat shrinkable tubing.

3. The electrical inductive apparatus of claim 1 wherein the at least one electrical bushing assembly is mounted in a substantially vertical position, and the second insulating means includes a tubular extension from the end of said bushing assembly which extends beyond the electrical connection between the encased end of the conductor of the bushing assembly and the first conductor, to form a tubular chamber sealed at its upper end and open at its lower end.

4. The electrical inductive apparatus of claim 1 wherein the predetermined level of the liquid dielectric provides an air space above the liquid dielectric, with the receptacle entering the liquid dielectric through at least a portion of the air space.

5. The electrical inductive apparatus of claim 4 wherein the liquid dielectric extends into the tubular receptacle to a predetermined level, with a sealed air space above said level.

6. The electrical inductive apparatus of claim 1 wherein the electrical connection between the first electrical conductor and the encased end of the' conductor of the electrical bushing assembly includes a tubular insulating member which extends outwardly from the end of the electrical bushing assembly and is filled with solid resinous insulating means.

7. The electrical inductive apparatus of claim 1 including a current limiting fuse connected in series with the second electrical conductor, between the electrical winding assembly and the second electrical contact of the receptacle.

8. An electrical transformer comprising a casing filled to a predetermined level with a liquid dielectric, a cover on said casing having openings therein for receiving protective fuse apparatus and at least one electrical bushing assembly,

a magnetic core-winding assembly positioned within said casing below the level of the liquid dielectric,

at least one electrical bushing assembly including an insulating body portion having first and second ends, and an axially extending electrically conductive stud member which is surrounded by said insulating body portion and extends between its ends, said insulating body portion being fixed to said cover, extending in sealed engagement through an opening therein, with its second end being within said casing,

protective fuse apparatus comprising a receptacle havceptable being fixed to said cover, extending in a sealed engagement through an opening therein, extending into said liquid dielectric for a predetermined distance, a fuse having first and second spaced electrodes connected by a fusible element, and a rod having one end attached to said fuse, said rod and fuse being removably disposed in said receptacle, sealing the upper end of its first opening, engaging the first and second electrical contacts with said first and second electrodes, respectively, and being sized to provide a radial space between said receptacle and said rod and fuse which enables the liquid dielectric to enter the receptacle and provide a predetermined air space above the liquid dielectric, a. first insulated conductor electrically connected between the encased end of the stud of said at least one electrical bushing assembly and said first electrical contact member, a second conductor electrically connected between said second electrical contact and said winding assembly.

first insulating means electrically insulating and sealing the electrical connection between said first eectrical conductor and the encased end of the stud of said at least one electrical bushing assembly to isolate the connection from ionized gas produced by said protective fuse apparatus,

and second insulating means electrically insulating and sealing the electrical connection between said first conductor and said first electrical contact.

9. The electrical transformer of claim 8 wherein the second insulating means is a heat shrinkable tubing.

10. The electrical transformer of claim 8 wherein the first insulating means includes an insulating tubular member which extends coaxially outward from the second end of the insulating body portion of the electrical bushing assembly.

11. The electrical transformer of claim 10 including solid resinous insulating means positioned within the outwardly extending portion of the insulating tubular member, which completely surrounds and embeds the electrical connection between the first insulated conductor and the encased end of the stud.

12. The electrical transformer of claim 8 wherein said second insulating means is a heat shrinkable tubing and the first insulating means includes an insulating tube which extends coaxially outward from the second end of the insulating body portion of the electrical bushing assembly, with solid resinous insulating means being fixed Within the outwardly extending portion of said insulating tubular member which completely surrounds and embeds the electrical connection between the first insulated electrical conductor and the encased end of the stud.

13. The electrical transformer of claim 8 wherein the elongated cylindrical body portion of the receptacle is continuous except for the second and third sealed openings in the side wall portion.

14. The electrical transformer of claim 8 wherein the first and second electrical contacts are spring loaded and fixed within insulated and sealed electrical contact holders. Y, Y

15. The electrical transformer of claim 8 including a current limiting fuse connected in series with the second electrical conductor, between the second electrical con- Lact of the receptacle and the electrical winding assem- References Cited UNITED STATES PATENTS 2,663,825 12/1953 Amundson 317-15 3,127,760 4/1964 Kirkpatrick et al. 73-1 3,178,613 4/1965 Dornbush et al 337-1 X BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner us. or. X.R. 337-1 

